The present invention relates to a printing apparatus. More specifically, the present invention relates to a printing apparatus having a duplex printing mechanism capable of forming a toner image on both sides of a sheet using a switchback method in which a rotational direction of a discharge roller is switched.
When a conventional printing apparatus performs a duplex printing operation, after an image forming process and an image fixing process are performed on one side (a first surface) of a sheet, a discharge roller rotates in a forward direction to transport the sheet toward a discharge outlet. Then, the discharge roller stops, so that a part of the sheet (a leading edge) is discharged from the discharge outlet.
Afterward, the discharge roller rotates in a reverse direction, i.e., performs a switchback, so that the sheet is pulled back in the conventional printing apparatus. Accordingly, the sheet is transported into a reverse path, so that a second surface of the sheet faces upwardly. After the sheet is reversed in the reverse path, the image forming process and the image fixing process are performed on a second surface of the sheet followed by discharging the sheet through the discharge outlet.
In the conventional printing apparatus, in a state that a part of the sheet is discharged from the discharge outlet, an operator may think that the printing operation is completed, and pull out the sheet. In the conventional printing apparatus, when the operator pulls out the sheet, a sensor disposed at an inlet of the reverse path detects that the sheet does not reach the reverse path. Accordingly, the conventional printing apparatus falsely determines that a jam (a paper jam) occurs, and stops the printing operation. As a result, the conventional printing apparatus displays notice information on a display thereof for prompting the operation to remove the jam from the conventional printing apparatus.
When the notice information is displayed on the display, the operator opens a cover of the conventional printing apparatus, and closes the cover after the operator confirms that there is no jam. In the conventional printing apparatus, various sensors disposed in the conventional printing apparatus detect the opening and closing of the cover. After the various sensors detect that there is no jam in the conventional printing apparatus, the printing operation is resumed.
As described above, in the conventional printing apparatus, once the operator mistakenly pulls out the sheet, the conventional printing apparatus detects the pullout as the jam and stops the printing operation. Accordingly, in order to resume the printing operation, it is necessary to perform the operation including the opening and closing of the cover similar to a case that the jam actually occurs, thereby causing a trouble to the operator.
To this end, Patent Reference has proposed another conventional image forming apparatus. In the conventional image forming apparatus disclosed in Patent Reference, a stepping motor drives a discharge roller. When the discharge roller stops, a current flowing in the stopping motor is maintained for applying a load to the discharge roller. Accordingly, when the duplex printing operation is performed, it is possible to prevent a sheet from being pulled out during the switchback.
Patent Reference: Japanese Patent Publication No. 09-249342
As explained above, the conventional image forming apparatus disclosed in Patent Reference has the configuration for preventing the sheet from being pulled out. When the conventional image forming apparatus performs the duplex printing operation, however, a part of the sheet is still discharged from a discharge outlet. Accordingly, an operator still can pull out the sheet. When the operator pulls out the sheet, the conventional image forming apparatus stops the duplex printing operation, thereby making it necessary to resume the duplex printing operation.
In view of the problems described above, an object of the present invention is to provide a printing apparatus capable of solving the problems. In the present invention, when the printing apparatus performs the duplex printing operation, it is possible to continue the duplex printing operation without interrupting the duplex printing operation even when a sheet is pulled out after the printing operation is performed on one side of the sheet.
Further objects and advantages of the invention will be apparent from the following description of the invention.